The invention relates to a diaphragm pump comprising a working diaphragm that, during pumping movements, oscillates between a bottom dead center and a top dead center. The working diaphragm delimits a pump chamber between itself and a preferably concave pump chamber wall and when located at the top dead center position, the working diaphragm rests against the pump chamber wall.
Diaphragm pumps of the type named above are already known in various configurations. If such diaphragm pumps are operated in the lower vacuum range, there is the risk that the working diaphragm will bulge due to differences in the pressure loads occurring between the top side and the lower side of the diaphragm and therefore will reduce the suction chamber volume. Even in this lower vacuum range, large pressure differences occur between the top side and the lower side of the diaphragm. While atmospheric pressure usually applies a load on the lower side of the diaphragm, the corresponding evacuation pressure acts on the top side of the diaphragm, wherein the maximum pressure difference is given by the atmospheric pressure minus the limiting pressure of the diaphragm pump.
In typical diaphragms of conventional diaphragm pumps, especially when these diaphragm pumps operate within the range of the limiting pressure and large differences in pressure loads are applied to the diaphragms, it is to be emphasized that the lateral, elastic zone of the flexible diaphragm bulges in the direction towards the feeding chamber due to the atmospheric pressure. This “bulging” of the diaphragm leads to the result that the suction chamber volume is reduced considerably, which has a negative effect on the suction capacity of diaphragm pumps.
This change in shape is especially pronounced in two-stage and multi-stage diaphragm pumps with low limiting pressures. In these pumps, the lowest vacuum stage is affected the most, because the greatest pressure differences occur here.
From, WO 00/49293, a membrane pump with a working membrane made of an elastic material is already known, which has in a strengthened central area for a connection for a connecting rod head and an outer area with a clamping rim for connection to the pump head. On the pump chamber defining upper side of the membrane, a number of circumferentially extending ribs are provided that are spaced apart from one another radially outwardly from the strengthened central area of the membrane, which provide a higher strength for the membrane against pressure while retaining the flexibility of the central area bordering the outer ring zone of the membrane.
With the help of the upper membrane side of the known membrane provided with ribs, it is possible for a cracking of the membrane upper side-, a bulging of the membrane between the clamping rim and the central area in the provided flexible ring zone is not prevented in any case by the circumferentially oriented ribs.